The overall goal of this research project is to assess whether specific developmental toxicants (e.g. trichloroethylene (TCE) and (As) arsenic) perturb one or more developmental pathways leading to morphologic alterations resulting in specific birth defects. Our main objective is to investigate is to investigate the molecular pathways altered by TCE that cause cardiac malformations in rat embryos. Our hypothesis is that analysis of markers at the molecular level will provide a sensitive index of environmental exposure. When these markers are chosen by empirical observation of altered expression, they are likely to indicate specific developmental pathways that are perturbed by toxicant exposure. As markers, these molecules can by used for promoter analysis and continued investigations into more proximally affected molecules in the tissue. Molecules critical to normal development can eventually be tested by genetic manipulation as a direct source of defects. Furthermore, we shall examine the similarities and differences of a separate potential teratogen (As versus TCE) in the developing embryos. Preliminary data indicate that several markers of exposure to TCE and As are perturbed in both heart and lungs during development. The PCR-Select subtractive hybridization technique that has been successfully used in our laboratory for TCE will also be used to isolate markers for As exposure. We propose to carry out the following specific aims: 1. Identify the distribution and timing of gene expression for four specific clones that were selected by screens for differential expression after exposure to teratogenic doses of TCE. The hypothesis is that miss-expressed molecules during developmentally significant patterns play a functional role in producing in producing heart defects. 2. Evaluate the sensitivity of altered marked expression in embryos exposed to varying levels of toxicants in maternal drinking water. Our objective is to determine minimum exposure levels that result in altered gene expression and use the most sensitive markers for risk assessment. 3. Clone the promoter region of the markers identified in aim 1. Identification of shared motifs would enable identification of molecules more proximal to the teratogenic activity of TCE. 4. Test the potential relationship between TCE exposure and the NMDA (N-Methyl-D-Aspartate) glutamate receptor and/or NFATc pathways as a mechanism of TCE teratogenicity. The hypothesis is that TCE-mediated heart defects may be caused by alterations in Ca++ flux involved with both molecules. 5. Identify and characterize markers of As exposure in developing embryos.